"Ziman, Steve (SDZI)" 04/08/02 11:55 AM To: John Silvasi/RTP/USEPA/US@EPA cc: "Walker, R C Robert (RCWalker)" , "'hermanrw@bp.com'" , Tom Helms/RTP/USEPA/US@EPA Subject: FW: AWMA paper John This paper, which was given at AWMA, essentially has the same information as the graph I shared with you at the meeting last week. It shows that for the 80 ppb cutoff, areas across the nation that had enough data to look at, are much more VOC limited than NOx limited. This is different than when a 120 ppb cutoff is used. As I mentioned, this may be due to the fact that many of the peak episodes for the one-hour standard go on for a few days, and exhaust available NOx relative to VOC availability. But, for episodes which do not exceed the one-hour standard, but might the 8-hour standard, the duration of the episode is probably such that available NOx is not exhausted. These latter episodes are probably short duration, which is a function of meteorology. Thus, solving for the one-hour 120 ppb may be solving a problem in which one or more types of meteorology drive the problem (i.e.., multiple day stagnation events), but it will not address the issue of other meteorology which leads to 80 ppb exceedances, but not 120 ppb. And in that situation, NOx reductions can exacerbate the problem rather than help it. You can place this in the docket. I also suggest that you look at the ARB web site on the weekday/weekend effects: http://www.arb.ca.gov/aqd/weekendeffect/weekendeffect.htm Most of the papers in this site, for the Feb 20 meeting, show that the weekend effect is a function of large decreases in NOx emissions during Saturday and Sunday, due to decrease in diesel heavy duty vehicles. What this finding shows is that for VOC limited areas, there is a real effect of the NOx reductions. I expect that this is good evidence that when an area is predominately VOC limited, as many will be for the 80 ppb standard, we will be doing the wrong thing by using NOx reduction, or a combination of VOC and NOx. So, one must be very careful with development of any 8-hr guidance, and make sure that any prescription, if any is included, have a sound technical basis. Steve Ziman, Ph. D. Sr. Staff Scientist Air Issues and Technology ChevronTexaco Energy Research and Technology Co 100 Chevron Way, Richmond, California 94802 sdzi@chevrontexaco.com phone 510-242-1530 fax 510-242-5577 -----Original Message----- From: Charles Blanchard [mailto:cbenvair@pacbell.net] Sent: Friday, April 05, 2002 11:21 AM To: Steve Ziman Subject: AWMA paper Steve - Attached is the AWMA Annual Meeting manuscript (June, 2001). The figure is not in this paper, but the same information is contained in the two tables. -- Charlie __________________________________ Charles L. Blanchard Envair 526 Cornell Ave Albany CA 94706 phone (510) 525-6231 fax (510) 528-2834 e-mail cbenvair@pacbell.net